1. Field of the Invention
The present invention relates to a method and apparatus for fractionating charged macro-molecules such as DNA using asymmetric pulsed field electrophoresis.
2. Related Art
The analysis and fractionation of large DNA molecules is a central step in large scale sequencing projects. Conventionally, gel electrophoresis is used to fractionate DNA molecules according to their sizes. This method includes two steps: sample loading and fractionation. First, sample solution containing DNA is loaded into loading wells in the gel slab before the electric field is turned on. Then, an electric field is applied. The DNA molecules move in the opposite direction of the electric field because they are negatively charged. As the electric field is applied, DNA molecules travel at different speeds according to their sizes, but the directions in which they migrate are always the same. Eventually, sample DNA molecules are separated into different bands, each of which contains DNA molecules of the same size, as shown in FIG. 1. Shorter DNA fragments move faster than longer ones. Therefore, they are separated according to their sizes. However, this standard method only works effectively for DNA molecules smaller than 40 kbp. Above this range, the standard method has to be modified. In particular, the applied electric field can no longer be DC, but is made to alternate between two different orientations. This modified scheme (pulsed-field gel electrophoresis) is routinely used in modern molecular biology laboratories, but it typically takes a few days to fractionate one set of DNA samples.
What is needed, and has not heretofore been provided, is a method and apparatus for quickly, or even continuously, fractionating charged macro-molecules.